1. Field of the Invention
The present invention relates to a semiconductor device and semiconductor device data write method and, more particularly, to an MRAM (Magnetic Random Access Memory) having an MTJ (Magnetic Tunnel Junction) element which stores “1” or “0” information by the TMR (Tunnel Magneto-Resistance) effect.
2. Description of the Related Art
Magnetic random access memories (to be referred to as MRAMs hereinafter) utilizing the TMR (Tunnel Magneto-Resistance) effect are recently considered promising as high-speed, large-capacity storage media.
In such an MRAM, as shown in FIGS. 10 and 11, a first write wiring line (e.g., bit line) WL1 and second write wiring line (e.g., word line) WL2 are arranged to run perpendicularly to each other. An MTJ (Magnetic Tunnel Junction) element 10 is arranged at the intersection of the first and second write wiring lines WL1 and WL2. The MTJ element 10 is formed from a fixed layer 11, a free layer (recording layer) 13, and a tunnel insulating film 12 sandwiched between the fixed layer 11 and the free layer 13.
In the MRAM, in order to write “1” data or “0” data in the MTJ element 10, one end of the first write wiring line WL1 is set to the ground potential, and the other end is set to a ±potential, as shown in FIG. 12. Currents I1 and I3 flow through the first write wiring line WL1 in two directions.
More specifically, as shown in FIG. 10, transistors Tr1a, Tr1b, Tr2a, and Tr2b are arranged as write switching elements at the two ends of the first write wiring line WL1. One end of the current path of each of the transistors Tr1b and Tr2b is connected to the ground terminal.
The first write wiring line WL1 allows the write current I1 to flow by using the transistors Tr1a and Tr1b, and the write current I3 to flow by using the transistors Tr2a and Tr2b. In this manner, the write currents I1 and I3 flow through the first write wiring line WL1 in two directions.
In this conventional MRAM, the current I1 is supplied to the first write wiring line WL1, and the current is supplied to the second write wiring line WL2, writing, e.g., “0” data in the MTJ element 10. After that, the current I3 in a direction opposite to the current I1 is supplied to the first write wiring line WL1, and the current is supplied to the second write wiring line WL2, writing, e.g., “1” data in the MTJ element 10. In other words, data opposite to written data can be rewritten in the MTJ element 10.
However, data rewrite enables rewriting video data and the like, failing to protect copyrights. The MRAM as a new storage medium is required to realize a structure which inhibits rewrite of written data.